1. Field of the Invention
The present invention relates to a defuzzifier circuit which converts fuzzy quantities into a determined value in hardware that executes fuzzy reasoning.
2. Description of the Prior Art
Fuzzy information obtained as a result of fuzzy reasoning appears in the form of electric signals distributed over a plurality of lines. Accordingly, it is necessary in order to control an actuator or the like by using these signals to convert them into a manipulated variable. A converting mechanism designed for this purpose is called defuzzifier. In general, the conversion is performed by arithmetically determining the center of gravity of fuzzy quantities (JP Appln No. 63-206007, 1988).
The prior art will be explained below on the basis of the contents of the above-mentioned publication.
One example of fuzzy information will be explained with reference to FIG. 6. Elements of fuzzy information are denoted by x, and it is assumed that there are discrete values x.sub.1, x.sub.2, . . . x.sub.n-1, x.sub.n. These elements are output onto a plurality of signal lines l.sub.1, l.sub.2, . . . l.sub.n, respectively, and grades (functional values corresponding to variables) .mu..sub.1, .mu..sub.2, . . . .mu..sub.n corresponding to these elements are represented by analog voltages or current signals appearing on the respective signal lines.
In this case, the grades .mu..sub.1, .mu..sub.2, . . . .mu..sub.n are assumed to be represented by voltages. In FIG. 6, the center of gravity (position on t he X axis) of fuzzy information is given by ##EQU1## Accordingly, multiplication, addition and division are needed to obtain the center of gravity. Therefore, in order to obtain the center of gravity only by addition, which is relatively easy, Equation (1) is transformed into Equation (2), and the latter is adjusted so that the denominator in Equation (2) is 1, thus eliminating the need for division: ##EQU2## That is, if K is adjusted so that the denominator is 1, the center of gravity can be obtained from Equation (3): ##EQU3##
Referring to FIG. 7, which is a specific circuit diagram, voltages .mu..sub.1, .mu..sub.2, . . . .mu..sub.n representative of elements of fuzzy information are led out onto n signal lines l.sub.1, l.sub.2, . . . l .sub.n and then multiplied by the coefficient K in a variable-grade reasoning engine 1 to obtain fuzzy quantities K.mu..sub.1, K.mu..sub.2, . . . K.mu..sub.n, which are input to both a weighted summing circuit 2 and a simple summing circuit 3. In the weighted summing circuit 2, calculation of Equation (3) is executed to output a voltage signal representative of the center of gravity.
In the meantime, the simple summing circuit 3 executes calculation of the denominator of Equation (2) and inputs the result of the calculation to a voltage adjusting circuit 4. The other input terminal of the voltage adjusting circuit 4 is supplied with a voltage corresponding to the grade 1. Accordingly, in response to the output signal from the voltage adjusting circuit 4, the coefficient K in the variable-grade reasoning engine 7 is adjusted so that the output from the simple summing circuit 3 is 1 at all times.
According to the above-described prior art, a circuit portion of the fuzzy reasoning circuit which is related to electric signals distributed over a plurality of lines l.sub.1, l.sub.2, . . . l.sub.n is controlled so that the output signal from the simple summing circuit 3, which is supplied with the electric signals, is equivalent to 1. In this case, the membership function circuit is provided with a grade control means to control the grade of the membership function. In this type of control system, if there are two or more converting elements, these elements cannot share one membership function circuit with each other, so that a membership function circuit must be provided for each converting element. The reason for this is that there is no possibility that grade control signals from all the defuzzifiers will be identical to each other.
In addition, the prior art employs an FET as a feedback resistor of an operational amplifier to adjust the gains of the weighted summing circuit 2 and the simple summing circuit 3 so that the output from the simple summing circuit 3 is equivalent to 1. However, since the FET has no satisfactory linear characteristics, the required accuracy cannot be obtained, so that a costly variable-gain amplifier is needed in practice.
In the above-described prior art, there are cases where the product of a plurality of reasoning results is obtained as a finally demanded value. For example, if the volumetric efficiency K.sub.v of an internal combustion engine and the water temperature correction factor K.sub.w are obtained as determined values by fuzzy reasoning, the value that is finally needed is the product of K.sub.v and K.sub.w. In other words, it will be convenient if the output of the defuzzifier for the volumetric efficiency k.sub.v can be weighted by K.sub.w.
In addition, weighting necessitates processing of the reasoning results by using a costly multiplier. The weighting process will be explained below with reference to FIG. 8.
FIG. 8(a) is a block diagram showing the arrangement for weighting, and FIG. 8(b) shows input/output port assignment. Inputs INP 1, INP 2, . . . are input to a reasoning engine. 5 to reason a volumetric efficiency K.sub.v (OUT 0) according to rules (not shown). Similarly, an input INP 5 is input to a reasoning engine 6 to reason a water temperature correction factor K.sub.w (OUT 1) according to rules (not shown). Then, the two reasoning results are input to a multiplier 9 to obtain K.sub.v.K.sub.w.
FIG. 9(a) and 9(b) show a system that needs no multiplier. In this system, a volumetric efficiency K.sub.v (OUT 0) is reasoned in a reasoning engine 10, and the result obtained is input to an input port INP 0 to obtain K.sub.v.K.sub.w in a reasoning engine 12. However, these conventional weighting techniques are unsuitable because of an increased number of rules.